The present invention relates to an apparatus for electropolishing of a helix for a microwave tube, and more particularly to an apparatus for a uniform electropolishing of a helix for a precision microwave tube which is weak to vibration.
Traveling wave tubes are used in the field of microwave communication networks such as communication satellite broadcast. FIG. 1 is a cross sectional view illustrative of a conventional traveling wave tube The conventional traveling wave tube has a cylindrically shaped body accommodating a helix 6 which comprises a metal tape in the form of helix spirally extending along a longitudinal direction of the cylindrically shaped body. The helix 6 is terminated at input and output portions 41 and 42. The cylindrically shaped body of the conventional traveling wave tube has an emitter side which accommodates an electron gun 42 which emits an electron beam. The cylindrically shaped body of the conventional traveling wave tube also has a collector side which has a collector 45 so that the electron beam emitted from the electron gun 43 travels through the inside of the helix 6 to the collector 45. The helix 6 is applied with a radio frequency current. Actually, a majority part of the radio frequency current or the high frequency current flows in the surface region of the helix 6. The radio frequency current has an interaction with the electron beam 44 whereby the high frequency current is amplified and fetched from the output portion 42. The above helix 6 may be made of a metal such as molybdenum and tungsten. The helix 6 serves as a delay circuit of the traveling wave tube, for which reason the helix 6 is an important element which determines characteristics of the traveling wave tube. It is extremely important that the helix 6 has a precise pitch, a high cleanliness level and accurate dimensions or sizes. An efficiency of the traveling wave tube depends upon the smoothness of surface of the helix 6, for which reason the surface of the helix 6 is required to have a high smoothness. The helix 6 is smoothed by electropolishing thereof.
The helix 6 is then subjected to the electropolishing. FIG. 2 is a schematic view illustrative of a conventional apparatus for electropolishing of the helix of the traveling wave tube. The conventional electropolishing apparatus has an electropolishing bath 5 which is cylindrically shaped and filled with an electrolyte solution 4. The electropolishing bath 5 has a cathode 12 which is so cylindrically shaped as to have a co-axis with the cylindrically shaped electropolishing bath 5. The cathode 12 may comprise a metal plate in the form of cylinder such as stainless. The electropolishing bath 5 has a cathode which is also immersed into the electrolyte solution 4. The helix 6 is immersed into the electrolyte solution 4 and also positioned to extend along a longitudinal direction of the cylindrically shaped electropolishing bath 5. The helix 6 is electrically connected to an anode. A current of a few amperes is applied across the anode connected to the helix 6 and the cathode 12 for carrying out the electropolishing of the helix 6.
Conventional methods for the electropolishing of the helix are disclosed in the Japanese laid-open patent publications Nos. 7-159113 and 56-123400. FIG. 3 is a diagram illustrative of a structure of an electropolishing apparatus disclosed in the Japanese laid-open patent publication No. 56-123400. A sample 50 to be polished is fed by a pair of a feeder roll 52 and a roll 61 into an electropolishing bath 55 for further feeding by rolls 62 and 63 through the electrolyte solution in the electropolishing bath 55 and subsequent pick up by a pair of a feeder roll 53 and a roll 64. The sample 50 is subjected to the electropolishing during the feeding through the electrolyte solution in the electropolishing bath 55. A cathode 51 is provided in the electropolishing bath 55 so that the cathode 51 is immersed into the electrolyte solution and the cathode 51 faces to the sample 50 extending between the rolls 62 and 63. Currents are supplied via the feeding rolls 52 and 53 through the sample 50 and the electrolyte solution to the cathode 51. Namely, the current is applied between the sample 50 and the cathode 51 through the electrolyte solution for electropolishing of the sample 50. When the sample 50 is subjected to the electropolishing during the feeding of the sample 50 between the rolls 6 and 63, then the sample 50 is positioned closer to the cathode 51. In the above conventional electropolishing apparatus, the sample 50 to be electropolished is moved in the electrolyte solution 54.
The above conventional electropolishing apparatuses shown in FIGS. 2 and 3, however, have the following problems. The conventional electropolishing apparatus shown in FIG. 2 has a problem in variation in etching amount by which the helix is etched. The helix 6 has a helical structure of not less than 100 millimeters in length and a resistance of about 0.1 .OMEGA. cm, for which reason even if a constant current is applied, then a voltage drop appears thereby causing a variation in etching amount by which the helix is etched, for example, about 20 micrometers in thickness. In this case, it is no longer possible to use the helix electropolished by the above conventional electropolishing apparatus shown in FIG. 2.
On the other hand the movement of the helix causes disturbance in pitch of the helix. Since, however, the pitch of the helix provides a remarkably large influence to the characteristics of the traveling wave tube. A slight vibration of the helix may cause a disturbance in pitch of the helix whereby the yield of the helix is dropped.
In the above circumstances, it had been required to develop a novel apparatus for electropolishing to a helix used for a traveling wave tube free from the above problems.